The present invention relates to a thermal infrared array sensor for detecting a plurality of infrared wavelength bands.
FIG. 1A is a schematic perspective view illustrative of a conventional thermistor bolometer thermal infrared array sensor. FIG. 1B is a fragmentary cross sectional elevation view illustrative of a conventional thermistor bolometer thermal infrared array sensor of FIG. 1A. The conventional thermistor bolometer thermal infrared array sensor is disclosed by R. A. Wood, xe2x80x9cUncooled Infrared Image Arrays and Systemsxe2x80x9d, Semiconductors and Semimetalsxe2x80x9d, vol. 17, volume editors P. W. Kruse and D. D. Skatrud Academic Press, 1997, p. 103. The conventional thermistor bolometer thermal infrared array sensor is formed over a silicon substrate 308. The conventional thermistor bolometer thermal infrared array sensor comprises a diaphragm 301 and beams 302 and a read out circuit 307. The diaphragm 301 comprises a bolometer material thin film Vox 305 having a large temperature coefficient of zero-power resistance and protective films SiN 306 which sandwich and surround the bolometer material thin film Vox 305. The beams 302 mechanically support the diaphragm 301 so that the diaphragm 301 is floated over the upper surface of the read out circuit 307. The beams 302 are further provided with electric wirings which comprise metal thin films of NiCr having a low thermal conductivity, The read out circuit 307 is formed in an upper region of the silicon substrate 308. A full reflective film 304 is provided over the read out circuit 307. A cavity 309 is formed between the diaphragm 301 and the surface of the silicon substrate 308. An infrared ray 300 is incident into the diaphragm 301 and a part of the incident infrared ray 300 is absorbed into the SiN protective films 306 whilst a remaining part of the incident infrared ray 300 is transmitted through the diaphragm 301 and the cavity 309 to the full reflective film 304, whereby the remaining part of the incident infrared ray 300 is fully reflected by the full reflective film 304 and then absorbed into the SiN protective films 306. The absorption of the infrared ray 300 causes a temperature rising of the diaphragm 301. The temperature rising of the diaphragm 301 causes variation in a resistance of the bolometer whereby variation in voltage can be detected If a temperature of a sample is lower than the original temperature of the diaphragm 301, then the diaphragm 301 shows a heat radiation to cause a temperature drop of the diaphragm 301, whereby the resistance of the bolometer is varied. The infrared ray absorption band of the SiN protective films 306 is 10 micrometers wavelength band, for which reason the above thermal infrared sensor is operable in this wavelength band.
FIG. 2A is a schematic perspective view illustrative of a conventional ferroelectric infrared array sensor. FIG. 2B is a fragmentary cross sectional elevation view illustrative of a conventional ferroelectric infrared array sensor of FIG. 2A The conventional ferroelectric infrared array sensor is disclosed by C. H. Hansen, SPIE Proc. 2020 vol. 1993, p. 330. The conventional ferroelectric infrared array sensor has a hybrid structure of ferroelectric ceramics 401 and a read out circuit 402 which are electrically connected via bumps 403. An array of the ferroelectric ceramics 401 is provided on an infrared absorption layer 404. Electrodes 408 are provided on the ferroelectric ceramics 401. The electrodes 408 are electrically connected through the bumps 403 to the read out circuit 402. The infrared absorption layer 404 comprises a cavity layer 406 having a first surface on which an infrared absorption film 405 is provided and a second surface opposite to the first surface, where on the second surface, a full reflective film 407 is provided. The ferroelectric ceramics 401 are provided on the full reflective film 407. Each of the bumps 403 has an electric wiring 409 for electrically connect the electrode 408 to the read out circuit 402. The conventional ferroelectric infrared array sensor is different in infrared absorption mechanism from the thermistor bolometer thermal infrared array sensor of FIG. 1A. An infrared ray 400 is incident into the infrared absorption layer 404. A part of the incident infrared ray 400 is reflected by the infrared absorption film 405. A remaining part of the incident infrared ray 400 is transmitted through the cavity layer 406 to the full reflective film 407. The remaining part of the infrared ray 400 is reflected by the full reflective film 407 and then transmitted through the cavity layer 406 to the infrared absorption film 405 The reflected infrared ray 400 is absorbed into the infrared absorption film 405. The above two reflected infrared rays show interference to cancel to each other in the infrared absorption film 405 so that the infrared rays are absorbed into free electrons in the infrared absorption film 405. The absorbed infrared rays are converted into a heat which causes a variation in dielectric constant of the ferroelectric ceramics 401 of (Ba, Sr)TiO3. The variation of the dielectric constant of the ferroelectric ceramics 401 causes a voltage variation. This infrared array sensor has a uniform thickness of the cavity layer, for which reason all pixels can detect the same wavelength band.
FIG. 3 is a schematic perspective view illustrative of a conventional dual band HgCdTe infrared array sensor which is different from the thermal infrared array sensors us shown in FIGS. 1A and 2A. The conventional dual band HgCdTe infrared array sensor has a hybrid structure of a silicon read out circuit and a two dimensional HgCdTe photo-diode array. The conventional dual band HgCdTe infrared array sensor is capable of detecting two different infrared wavelength bands concurrently in the same pixel. The conventional dual band HgCdTe infrared array sensor is thus of a dual band quantum infrared array sensor, In FIG. 3, the illustration of the silicon read out circuit is omitted. The conventional dual band HgCdTe infrared array sensor is disclosed in U.S. Pat. No. 5,149,956 issued to P. R. Norton. Each pixel 501 is formed on a CdZnTe substrate 502 which is transparent to infrared ray. The each pixel 501 comprises an n-Hg0.7Cd0.3Te layer 503, a p-Hg0.6Cd0.4Te layer 504, and an n-Hg0,8Cd0.2Te layer 505. The n-Hg0.7Cd0.3Te layer 503 absorbs an infrared ray of a wavelength band of 3-5 micrometers. The n-Hg0.7Cd0.3Tc layer 503 has an energy band gap of about 0.24 eV and a thickness of 10 micrometers. The p-Hg0.6Cd0.4Te layer 504 has a larger energy band gap than the n-Hg0.7Cd0.3Te layer 503. The n-Hg0.8Cd0.2Te layer 505 absorbs an infrared ray of a wavelength band of 10 micrometers. The n-Hg0.8Cd0.2Te layer 505 has an energy band gap of about 0.1 eV and a thickness of 10 micrometers. An In bump 506 is provided to mechanically and electrically connect the n-Hg0.7Cd0.3Te layer 503 to the read out circuit not illustrated. An In bump 507 is provided to mechanically and electrically connect the p-Hg0.6Cd0.4Te layer 504 to the read out circuit not illustrated. An In bump 508 is provided to mechanically and electrically connect the n-Hg0.8Cd0.2Te layer 505 to the read out circuit not illustrated. The p-Hg0.6Cd0.4Te layer 504 extends over the entire of the array to serve as a common electrode. The n-Hg0.7Cd0.3Te layer 503 and the n-Hg0.8Cd0.2Te layer 505 are independently provided for each pixel, so that each pixel has an independent npn stricture so that each pixel 501 can detect infrared rays of two different wavelengths.
First and second infrared rays 500 having short and long wavelengths are incident to the CdZnTe substrate 502. The first infrared ray 500 having the short wavelength is absorbed into the n-Hg0.7Cd0.3Te layer 503 and the p-Hg0,6Cd0.4Te layer 504. The second infrared ray 500 having the long wavelength is absorbed into the n-Hg0.8Cd0.2Te layer 505. The first infrared ray 500 having the short wavelength is detected as a photoelectric current by a p-n junction between the n-Hg0.7Cd0.3Te layer 503 and the p-Hg0.6Cd0.4Te layer 504. The second infrared ray 500 having the long wavelength is is detected as a photoelectric current by a p-n junction between the p-Hg0,6Cd0.4Te layer 504 and the n-Hg0.8Cd0.2T layer 505. The detected photoelectric currents are transmitted through the indium bumps 506, 507 and 508 to the silicon read out circuit.
The thermal uncooled infrared array sensors shown in FIGS. 1A and 2A are disadvantageous in difficulty of plural infrared wavelength bands in the single device. The HgCdTe dual band infrared array sensor shown in FIG. 3 is disadvantageous in difficulty of three or more infrared wavelength bands and also in need to cool the device to operate the same.
In the above circumstances, it had been required to develop a novel thermal uncooled infrared array sensor free from the above problems.
Accordingly, it is an object of the present invention to provide a novel thermal uncooled infrared array sensor free from the above problems.
It is a further object of the present invention to provide a novel thermal uncooled infrared array sensor, wherein a single sensor is capable of detecting infrared rays of plural different wavelength bands.
The present invention provides an infrared array sensor having an array of infrared sensors of different plural types for detecting infrared rays of different plural wavelength bands.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.